[tex-live] Equation Problem

[snvv]

Hello

I have a problem with equations.
When I use the following code 
$\hat{\vartheta}_{t|t} = \hat{\vartheta}_{t|t-1}+K_{t}\varepsilon_{t}$

$\hat{\vartheta}_{t|t-1} = F\hat{\vartheta}_{t-1|t-1}$

$\varepsilon_{t}=y_{t}-\varphi_{t}^{\prime}\hat{\vartheta}_{t|t-1}$

$K=\frac{\sum_{t|t-1}\varphi_{t}}{\sigma_{e}^{2}+\varphi_{t}^{\prime}\sum_{t|
t-1}\varphi_{t}}$

$\sum_{t|t-1}=F\sum_{t-1|t-1}F^{\prime}+GWG^{\prime}$

$\sum_{t|t} =\sum_{t|t-1}-\frac{\sum_{t|
t-1}\varphi_{t}\varphi_{t}^{\prime}\sum_{t|t-1}}
{\sigma_{e}^{2}+\varphi_{t}^{\prime}\sum_{t|t-1}\varphi_{t}}$ \\

Then the equations are just fine

When I try to number the equations with the following code
\begin{subequations}\label{grp}
\begin{align}
\hat{\vartheta}_{t|t} = \hat{\vartheta}_{t|t-1}+K_{t}\varepsilon_{t}\\
\hat{\vartheta}_{t|t-1} = F\hat{\vartheta}_{t-1|t-1}\\
\varepsilon_{t}=y_{t}-\varphi_{t}^{\prime}\hat{\vartheta}_{t|t-1}\\
K=\frac{\sum_{t|t-1}\varphi_{t}}{\sigma_{e}^{2}+\varphi_{t}^{\prime}\sum_{t|
t-1}\varphi_{t}}\\
\sum_{t|t-1}=F\sum_{t-1|t-1}F^{\prime}+GWG^{\prime}\\
\sum_{t|t} =\sum_{t|t-1}-\frac{\sum_{t|
t-1}\varphi_{t}\varphi_{t}^{\prime}\sum_{t|t-1}}
{\sigma_{e}^{2}+\varphi_{t}^{\prime}\sum_{t|t-1}\varphi_{t}} 
\sum_{t|t-1}F
\end{align}
\end{subequations}

Then I have some problems.
1st the summation is to large (i.e see last equation in the attached file)
2nd the last equation is not numbered properly
3nd I use the xgreek package and the numbering in equations is in Greek (i.e 
1α instead of 1a)

is it possible to solve the above problems?

Thank you
snvb
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